Prior to the concern over energy efficiency and cost savings in building maintenance, many buildings, both residential and commercial, were constructed with a window assembly having a primary-glazing pane. In order to decrease thermal losses through window openings and increase the desirability and livability of these older buildings, either interior or exterior storm windows that create a multiple pane window unit are used.
Exterior storm windows are typically mounted on the exterior of the building to cover the primary glazing and shield it from the environment. Such arrangements have served to provide improved insulation, but are also subject to certain drawbacks.
The exterior storm windows are usually constructed of rigid, weather resistant materials, such as aluminum or other metals. These materials have relatively high thermal conductivity and, as a result, conduct heat away from the interior of the building and therefore do not permit maximum energy efficiency. In addition, the exterior storm windows can be difficult to install and can require expensive, professional installation due to things such as ground landscaping or the height at which the windows would have to be installed. In some commercial buildings the window elevations are so extreme that exterior storm windows are not available at all as a practical matter. With certain historic buildings and condominium dwellings, use of exterior storm windows is prohibited by law or restrictive covenant. Even when such storm windows can be easily installed, to apply them over casement or awning windows typically restricts or entirely eliminates the workability of those window assemblies.
U.S. Pat. Nos. 4,160,348 (Chapman et al.); 4,369,828 (Tatro); and 5,282,504 (Anderson et al.) disclose interior storm windows attached to the window frame at the interior of the building. Such storm windows have, for example, been held in place by magnetic strips or guide tracks secured to the window frame adjacent to the primary glazing pane. The interior storm windows can be employed at all building elevations and are substantially unnoticeable from the building exterior, thus overcoming many of the limitations on usage of the exterior storm windows. Further, because these storm windows are on the inside of the building, they do not need to be as weather resistant. Therefore, the interior storm windows can be constructed of materials that are less thermally conductive.
However, interior storm windows typically require careful, on-site measurement of each window and largely custom construction often with professional assistance. A finish trim often needs to be cut and stained at the site and installed separately from the storm window. Further, the interior storm windows often interfere with window hardware, such as handles and cranks for casement or awning windows. This hardware must be removed and the window assemblies rendered inoperative if the interior storm window is to be installed. Likewise, since interior storm windows are fixedly mounted to the window frame, the window's mounting frame and panes restrict access to the primary glazing pane for cleaning and/or removal of the primary glazing pane. Similarly, in window openings of lesser depth, use of the interior storm windows can preclude use of a Venetian blind or shade between the primary glazing pane and the storm window pane. Such between window mountings of blinds would otherwise be desirable to decrease the accumulation of dust on the blinds.